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General Questions Questions

Sorting through the definitions of mic and line level can be confusing because there are varied definitions of the terms among audio engineers and manufacturers.

Line level refers to the typical level (strength or amplitude) of the audio signal from tape decks, CD players, VCR's, mixers, signal processing equipment and other consumer and professional audio gear. There are two types of line level: consumer and professional. Consumer level line level is generally thought of as a signal whose level is at -10 dBV (0.316). CD players and VCR's are examples of consumer line level equipment. Professional line level is generally thought of as a signal whose level is at +4 dBu (1.23 volts or significantly higher). Signal-processing equipment and professional mixing consoles are examples of professional line level equipment.

Mic level is the typical level (strength) of a microphone signal. Mic level is generally significantly lower than line level, although that is not always the case. Depending upon the microphone and the sound pressure level (SPL) injected into the microphone, the level may range from a few microvolts for a whisper, up to several volts for a microphone in front of a guitar cabinet.

The Open Circuit Sensitivity specification tells how much electrical output a microphone produces in response to certain sound pressure input. If two microphones are subject to the same sound pressure level and one puts out a stronger signal (higher voltage), that microphone is said to have higher sensitivity. However, keep in mind that a higher sensitivity rating does not necessarily make one microphone better than another microphone with a lower sensitivity rating.

At Audio-Technica, we test Open Circuit Sensitivity by placing the microphone in a sound field with a frequency of 1 kHz at a sound pressure level of 1 Pascal (1 Pa, which is equivalent to 94 dB SPL); then we measure the voltage at the microphone's output terminals.

A note about decibels: In the audio world, a decibel (dB) is a mathematical shorthand that is used to represent how two different audio levels compare to each other. It is a logarithmic ratio (logarithms use powers of 10 to make large numbers smaller and easier to work with). Since decibels are about comparisons (comparing volts with volts, or watts with watts, for instance), a reference number is included with the decibel (often in the suffix). For example, dBV = dB referenced to 1 Volt. One decibel (1 dB) is generally thought of as the smallest change human hearing can perceive.

Back to Open Circuit Sensitivity. Our AE3000 cardioid condenser microphone has an Open Circuit Sensitivity of -43 dB (7.0 mV) re 1V at 1Pa. This specification means that a 1 kHz tone played at a sound pressure level of 1 Pascal produces a voltage of 7.0 milivolts. Please note we state the output voltage in decibels referenced to 1 volt (dB re 1V) by using the following formula 20Log(0.007)= -43.098 dBV.

Feedback occurs when the amplified sound from any loudspeaker reenters the sound system through a microphone and is amplified again and again, causing a loop. To avoid or lessen the likelihood of feedback, try some of these steps:

- Keep the microphone behind the loudspeakers to minimize the sound that can reenter the microphone. If the microphone is in front of the speakers, then feedback is nearly guaranteed.
- Use a microphone with a unidirectional (cardioid) polar pattern. A cardioid microphone has its maximum rejection at the rear of the mic. Keep monitors or loudspeakers in this area of maximum rejection.
- Place the microphone close to the sound source. When you reduce the distance between the sound source and the microphone by half, you double the sound pressure level at the microphone. This increases your gain before feedback (i.e., it allows your sound system to produce more SPL before reaching a level that would induce feedback).
- Use an equalizer or feedback eliminator to dampen the frequencies where feedback is occuring.

A restring kit is available through Audio-Technica U.S. (email parts@atus.com). For instructions on how to restring the AT8410a shock mount, click here. For instructions on how to restring the AT8441 and AT8449 shock mounts, click here.